A recent significant advancement in the field of gas lancing is the development of the coherent jet technology disclosed, for example, in U.S. Pat. No. 5,814,125—Anderson et al. and in U.S. Pat. No. 6,171,544—Anderson et al. In the practice of this technology one or more high velocity gas jets ejected from one or more nozzles on a lance are maintained coherent over a relatively long distance by the use of a flame envelope around and along the high velocity gas jet(s). The flame envelope is formed by combusting fuel and oxidant ejected from the lance respectively from two rings of ports, an inner ring and an outer ring, around the high velocity gas jet nozzle(s). The ports are oriented in line with, i.e. parallel to, the lance axis. Typically the fuel for the flame envelope is ejected from the inner ring of ports and the oxidant for the flame envelope is ejected from the outer ring of ports. An extension on the lance perimeter forms a protected recirculation zone into which the high velocity gas jet(s) and the flame envelope fluids are provided from the nozzle(s), and ports. This recirculation zone enables some recirculation of the ejected fluids enabling improved ignition and improved stability of the flame envelope, thus enhancing the coherency and thus the length of the high velocity gas jet(s). The coherent jet(s) can be used to deliver gas into a liquid, such as molten metal, from a relatively long distance above the surface of the liquid. One very important application of this coherent jet technology is for providing oxygen for use in steelmaking operations such as electric arc furnaces and basic oxygen furnaces.
The recirculation extension, though constituting an improvement over earlier coherent jet systems, introduces certain problems concerning lance design and lance lifetime due to the need to water-cool the tip. These problems are of particular concern when the coherent jet system is used in a very harsh environment such as a basic oxygen furnace.
Accordingly, it is an object of this invention to provide an improved coherent jet system.
It is another object of this invention to provide a system which can produce effective coherent gas jets without the need for a lance extension or other element to establish a recirculation zone for the gases ejected from the lance.